Not so.
Only the overly inclusive definition of evolution put forward by creationists which includes abiogenesis and the 'big bang' cosmology can be considered in any way 'atheistic'. Darwin said nothing about abiogenesis or the beginnings of the universe in his initial ToE offering. As far as I know, we are arguing the Theory of Evolution as put forward by the neo-darwinian synthesis on these threads. This is not about 'origins' or atheism.
It may be that many of us (pro-evos) do believe that abiogenesis took place and the universe is the result of an unaided 'big bang' but the discussion of those concepts is initiated by the anti-evolutionists not by the proponents of evolution. It may be true that many of us are indeed atheists but nowhere in the Synthesis will you find the origin of the universe or the origin of life mentioned.
Only if you consider a terrestrial old age to be atheistic can you consider the ToE to be atheistic. In that case you would also have to consider the geological and astronomical sciences to be atheistic as well.
Are you a theist who also believes in evolution?
If so, can you describe that particular God? Thanks.